A Level Resits

I can almost guarantee you at least someone has gotten into one of those 3 through resitting and without mitigating circumstances - most likely king's.

UCL are happy to consider resit applicants, even without mitigating circumstances, for some courses.
The best way to find out would be to either check their course page or, if it is not clear there, email the admissions department for your course of choice.

Ahh thank you for this! I certainly hope that they are! The only thing that throws me off is that I would initially be applying with predicted grades (and achieved from this year) and then I would sit the exams next year, so I'm not sure whether they'd give me an offer based on a new set of predicted grades, as I'd have my new A Level grades next August.

If they were to give you an offer, I'd imagine it would be a conditional one based on a new set of predicted grades. Then, you would be expected to meet these requirements next August.

If the offer was AAA and you'd achieved ABB this year, for example. You'd ask to be predicted As in the subjects you received Bs in. Then, you would have already have satisfied the first A of the condition and be expected to satisfy the further As next year. Some courses at some Unis want to see all 3 A levels taken in the same year, however. So you should probably also double check this first.

Thank you so much for your response, you've clarified a lot of stuff! I have a lot of emailing to do now...

Good to hear. Good luck with your applications!